Activists trying to bring aid to Gaza today claimed their boat had been rammed by Israeli gunboats in a "criminal attack" in international waters.

The Free Gaza Movement said its vessel, the Dignity, was intercepted by several Israeli ships as it headed to the Gaza Strip, which has been under Israeli aerial bombardment since Saturday.

One gunboat rammed the Dignity on the port bow side, causing heavy damage, although no one was hurt, the group said.

"When attacked, the Dignity was clearly in international waters, 90 miles off the coast of Gaza," the group said on its website. "The gunboats also fired their machine guns into the water in an attempt to stop the mercy ship from getting to Gaza.

"Israel thumbs its nose in the face of maritime law by attacking a human rights boat in international waters and has put all of these human rights observers at risk.

"At no time was the Dignity ever close to Israeli waters. They clearly identified themselves, and the Israeli attack was wilful and criminal."

The group said the attack took place as the Dignity carried 16 passengers and three tonnes of medical supplies at the request of doctors in Gaza.

The crew and passengers had hoped to treat some of those injured in four days of the Israeli air strikes, with hospitals in the territory overwhelmed.

The Dignity later arrived in the Lebanese port of Tyre, where it was met by cheering crowds.

Lubna Masarwa, a Free Gaza spokeswoman, said the boat had gone to Lebanon – despite Israeli navy orders that it sail to Cyprus – because of a lack of fuel.

Masarwa said the ship was "in bad shape" due to damage sustained in the collision and was taking on small amounts of water.

The Lebanese president, Michel Suleiman, ordered that the Dignity be "rescued" and welcomed back in Lebanon.

Markos Kyprianou, the Cypriot foreign minister, told public radio his country would lodge a formal protest over the incident.

He said that although the boat was neither Cypriot-owned nor Cypriot-registered, the fact that it left Cyprus and had Cypriot nationals on board accorded the government "the right to be informed and to protest".

Kyprianou said he had instructed the Cyprus embassy in Israel to lodge the protest.

The Dignity flies the flag of Gibraltar and is piloted by an English captain. Its 16 passengers include Cynthia McKinney, a former US congresswoman.

It left for Gaza from Lanarca in Cyprus yesterday. The group said journalists on board filmed the attack.

An Israeli foreign ministry spokesman, Yigal Palmor, told Reuters there had been no shooting, although two ships had made "physical contact".

Palmor said the boat had failed to respond to Israeli naval radio contact and an Israeli vessel had "clashed with the ship". He said nobody was hurt, and the Israeli ship escorted the aid boat back to Cypriot territorial waters.

Israel declared the coastal territory a closed military zone after it launched air attacks on Hamas targets in Gaza on Saturday in response to Hamas firing rockets into Israel. Israel said the Free Gaza movement boat would not be permitted to dock in the Gaza Strip.

The Free Gaza group has made five boat deliveries of aid to Gaza since August, defying a blockade imposed by Israel when Hamas won control of the territory in June 2006.

Aid ships for the Palestinian coastal territory often stop at Cyprus before heading to Gaza, opting for the indirect route to deprive Israel of any excuse not to allow them in.

The last boat to make the trip on December 20 carried a Qatari delegation, Lebanese activists and journalists from Israel and Lebanon. Qatar has good relations with both Israel and Hamas.

More than 360 Palestinians have been killed in the Israeli attacks on Gaza since Saturday. In the same period, four Israelis have died in rocket strikes from Gaza.

The UN relief and works agency, which supports Palestinian refugees and has large programmes in Gaza, said 62 civilians were dead at a conservative estimate.

The overall number of injured is thought to be as high as 1,400 although Gazan hospitals are so overcrowded and short of medicine and equipment that they are turning away all but the most seriously wounded.